A longstanding continuing need has existed for a truly effective speed changing device for mechanical systems, particularly those which are gearless, commonly referred to as traction drives. Most available traction drive systems are limited to a speed change ratio in the order of 10 to 1, and even with such a low ratio do not exhibit the properties of low backlash, high torque capacity and high efficiency.
Often, traction drive devices employ epicyclic drive members with a series of planetary members encircling a sun member. Rotational motion is transmitted via the sun member with highly concentrated loading on the surface of the sun member. Torque is limited in such systems, the system tends to have lower efficiency than is desired and the energy lost is converted to heat in the region of the sun member at the innermost region of the system and difficult to remove. Such systems also exhibit a significent amount of backlash unless they are loaded so severely that efficiency suffers.
A number of prior researchers have attempted through the years to improve traction drive systems and in the process have improved one characteristic, usually at the sacrifice of other parameters of the system.
Desired is a traction drive system which achieves all of the following:
1. A high speed change ratio, e.g. up to and greater than 100:1; PA1 2. Low backlash; PA1 3. Linearity of speed between input and output; PA1 4. High efficiency; PA1 5. Easily cooled; PA1 6. High torque capability; PA1 7. Balanced loading within the system; PA1 8. Freedom from harmonics; and PA1 9. Concentricity of input and output.
Additionally, it is often desired that an annular configuration be possible for the drive system.
Heretofore, the geared system has been selected where high torque transfer is required and high speed change ratio desired. The geared system, however, has inherent backlash which eliminates its use where precision non-backlash is needed or where freedom from harmonics is essential. Examples of geared speed change systems are shown in the following U.S. patents:
______________________________________ 4,228,698 M. E. Winiasz October 21, 1980 4,155,276 W. H. Fengler May 22, 1979 4,016,780 S. J. Baranyi April 12, 1977 3,424,036 W. L. Colgan Jan. 29, 1969 3,330,171 A. L. Nasvytis July 11, 1967 3,442,158 E. Marcus May 6, 1969 ______________________________________
Where harmonic suppression and reduced backlash is desired at the loss of torque handling ability, the traction drive has been adopted. Examples of such systems appear in the following U.S. patents:
______________________________________ 4,128,016 A. L. Nasvytis Dec. 5, 1978 4,112,787 H. Tippmann Sept. 12, 1978 3,941,004 C. E. Kraus March 2, 1976 3,889,554 B. J. Sinclair June 17, 1975 3,848,476 C. E. Kraus Nov. 19, 1976 3,254,546 A. L. Nasvytis June 7, 1966 3,286,550 C. Rosain et al Nov. 22, 1966 3,216,285 A. L. Nasvytis Nov. 9, 1965 2,837,937 C. E. Kraus June 10, 1958 2,656,737 G. L. Lang Oct. 27, 1953 ______________________________________
Each of these systems offer the general advantages of traction drives but exhibit the traditional limitations of traction drive systems outlined above. Continued research to the date of my invention has failed to meet the full needs for traction drives.